It has long been the practice to enhance physical security at various installations by providing barriers constructed of barbed entanglement devices. These barriers usually take the form of helical coils of barbed materials which are placed atop walls and fences or arranged in stacked arrays between walls and that fences. The oldest, and most common, form of barbed barrier is that made from barbed wire. Characteristically, barbed wire is only barely self-supporting and therefore can be crushed from a coil form with very little effort. Such barriers usually can be breached with simple aids such as a heavy cloth or a board. Moreover, the rather flimsy appearance of the barbed wire and the fairly short, non-lethal, barbs thereon, often fail to discourage a person from attempting to breach the barrier. It has thus been recongnized that for secure installations more rugged and more intimidating barriers are required. This has led to the development of barbed tape barriers.
There are two types of barbed tape in common use today. The first of these is usually referred to as "Barbed Tape Concertina" and is formed by clinching a strip of barbs over a high tensile, spring steel wire which is preformed to the desired helical configuration. This type of tape is disclosed in U.S. Pat. No. 2,908,48, granted Oct. 13, 1959 to S. Uhl for "BARBED WIRE SPIRAL" and U.S. Pat. No. 3,916,958, granted Nov. 4, 1975 to S. Uhl for "PROCESS AND APPARATUS FOR PRODUCING A BARBED SPIRAL". One disadvantage to this type of barbed tape is its cost, which is relatively high because of the requirement that spring quality steel be used for the supporting wire core of the tape. This tape is also deficient in its performance because the barrier convolutions are relatively weak in vertical compression. Even though it is the usual practice to clip together adjoining convolutions at spaced intervals to impart structural integrity to the barrier, simple breaching aids usually are sufficient to subvert the purpose of the barrier. Lastly, the short barbs usually provided on this type of tape and the "skinny" appearance of the tape render the tape only slightly more intimidating than ordinary barbed wire. Thus this tape fails to discourage attempts to breach it.
The other form of barbed tape in common use today is that known generally by its military designation of "General Purpose Barbed Tape Obstacle", or "GPBTO". This barrier consists of a unitary flat metal strip which is bent edge wise in the form of a helix and has portions cut away so that elongated barbs are provided at spaced intervals along the two edges of the strip. In some of these barriers the strip is formed with a continuous uniform arcuate curvature as disclosed in U.S. Pat. No. 3,463,455, granted Aug. 26, 1969 to P. T. Meckel for "HELICAL BARBED TAPE UNIT". Other barriers of this type are formed by edge bending the strip into identically angularly displaced adjoining linear segments to form the helix. Such a tape is disclosed in U.S. Pat. No. 4,040,603, granted Aug. 9, 1977 to M. R. Mainiero for "BARBED METAL TAPE". The method for manufacturing this tape is disclosed in U.S. Reissue Pat. No. 30,814, reissued Dec. 8, 1981 to M. R. Mainiero for "APPARATUS AND METHOD FOR FORMING BARBED TAPE". The Meckel patent and the Mainiero patents disclose techniques for providing shallow reinforcing channels or grooves throughout the linear extent of the tape strip, presumably for the purpose of rigidifying the resulting barrier. Not withstanding such reinforcement, barriers formed in the manner taught by Meckel and Mainiero are required to be fabricated from either expensive, spring quality, austenitic stainless steel materials or of lower quality steel in a thicker strip in order to possess sufficient strength to resist collapsing forces from breach attempts. Furthermore, in order to control bending of the strip of metal stock used to manufacture the Mainiero tape, it is usually necessary to punch holes in the tape at the bend locations and such holes further weaken the tape in edgewise bending.
One technique for reducing the breachability of the GPBTO barrier is to attach spacer wires between corresponding points on successive convolutions of the barrier. This is described in the aforementioned Meckel patent. Another technique that has been employed for this purpose is to fasten, weld together, or otherwise secure corresponding points on successive convolutions much in the same manner as has been done with Barbed Tape Concertina and described in the aforementioned Uhl patents. The attachment of spacer wires and the fastening or welding together of the convolutions of a helical barrier both present complex manufacturing problems which contribute greatly to the cost of the complex barriers.
Further efforts to improve the intimidation factor and to reduce the breachability of barbed tape barriers has resulted in a second helical tape being disposed inside the outer, or main helical tape. The aforementioned Meckel patent discloses a GPBTO barrier with this construction. U.S. Pat. No. 3,155,374, granted Nov. 3, 1964 to G. Sieffert for "PLAIN OR BARBED WIRE DEFENSE COIL", discloses a Barbed Tape Concertina with one helix inside another. Of course, with any dual helix barrier, means must be provided for supporting the inner helix on the outer helix and this means that additional cumbersom and costly wires, fasteners or welds must be incorporated into the barrier.
There continues to be a need for an effective barbed tape barrier which can provide all of the advantages of the Barbed Tape Concertina and the GPBTO barrier, but which can be efficiently and inexpensively manufactured and is rugged and intimidating in use.